In blood culturing, the machine alerts us when the level of carbon dioxide increases. This indicates that there is most probably multiplication of micro organisms in a particular blood culture bottle.
Suppose the patient's specimen revealed scanty GPC in chains.
Could you offer a reason why a Gram done on the blood culture bottle may show no organisms. Even though the machine sounded an alert.
The acid fast smear shows AFB. Growth on selective agar is negative after 6 weeks.
Suggest a few reasons why this may be.
Wednesday, March 16, 2011
ELEK test
This test is done to determine if an already isolated and identified Corynebacterium diphtheriae produces toxins.The plate comprises molten agar, rabbit serum (for enrichment) and potassium tellurite. Place a filter paper strip impregnated with antitoxin across the middle of the plate. Allow the filter paper to sink to the bottom of the plate. Let the plate solidify and ensure that it is dry before use.
All inoculations are done at right angles to the long edge of the filter paper. All inoculations are done parallel to each other. Finally ensure that the test organism is next to the positive control. The inoculations are line streaks.
After incubation (18-24 hours at 37 degrees) examine the plate for white lines of precipitation that extend outwards from the line of inoculation/bacterial growth at an angle of 45 degrees. If you inoculated the test next to the positive control, and if the test is positive, you will see a wave like formation.
All inoculations are done at right angles to the long edge of the filter paper. All inoculations are done parallel to each other. Finally ensure that the test organism is next to the positive control. The inoculations are line streaks.
After incubation (18-24 hours at 37 degrees) examine the plate for white lines of precipitation that extend outwards from the line of inoculation/bacterial growth at an angle of 45 degrees. If you inoculated the test next to the positive control, and if the test is positive, you will see a wave like formation.
Nagler plate
This is a test done to determine if Clostridium perfringens produces lecithinase, a toxin.
The agar plate is egg based which provides the lecithin. Its colour is similar to a nutrient agar plate. These plates dont have a long shelf life so are either made up in small quantities of made when required. the plates need to be sealed in plastic bags and refridgerated prior to use. Allow plates to reach room temperature before use.
divide the plate in half using a permanent marker. Name one half as the seeded portion. Seed that half with the lecithinase.
Streak your test organism, positive and negative controls perpendicular to the dividing line, parallel to each other, using a line streak. Ensure that you start streaking from the unseeded half to the seeded half. This is so that no lecithinase is carried over to the unseeded half.
Incubate the plates anaerobically for 18-24 hours at 37 degrees.
When lecithin combines with lecithinase, it produces opalescence, which has a cloudy, milky, opal looking effect. Therefore a positive reaction would be opalescence on the unseeded half, and no opalescence on the seeded half. Very pretty!!in the seeded half, the lecinthinase is neutralised by the antitoxin, thats why no opalescence is seen.
Ensure that before reading your test you read the positive and negative controls.
The agar plate is egg based which provides the lecithin. Its colour is similar to a nutrient agar plate. These plates dont have a long shelf life so are either made up in small quantities of made when required. the plates need to be sealed in plastic bags and refridgerated prior to use. Allow plates to reach room temperature before use.
divide the plate in half using a permanent marker. Name one half as the seeded portion. Seed that half with the lecithinase.
Streak your test organism, positive and negative controls perpendicular to the dividing line, parallel to each other, using a line streak. Ensure that you start streaking from the unseeded half to the seeded half. This is so that no lecithinase is carried over to the unseeded half.
Incubate the plates anaerobically for 18-24 hours at 37 degrees.
When lecithin combines with lecithinase, it produces opalescence, which has a cloudy, milky, opal looking effect. Therefore a positive reaction would be opalescence on the unseeded half, and no opalescence on the seeded half. Very pretty!!in the seeded half, the lecinthinase is neutralised by the antitoxin, thats why no opalescence is seen.
Ensure that before reading your test you read the positive and negative controls.
Monday, March 14, 2011
foundation immunology theory test 1 comments
Hi. These are some comments that i feel compelled to make after marking your scripts and reviewing your answers.
The test comprised just 5 questions. Yes I concede that the question on Ab structure was trickery but that was done deliberately to test your knowledge. You were/are supposed to be aware of the fact that IgM is a pentamer. When I questioned you in class during the practical session, you all agreed that you knew this. But knowing this fact and applying it are two different things.
Question 4 was done very poorly. I really emphasized in class that cells express cell markers. CD1 is a maturation marker and is only expressed by thymocytes. Thymocytes are immature T cells found only in the thymus. Thats 2 marks out of 5. The remaining 3 marks comes from stating that CD25 is only expressed by an activated/stimulated cell; a thymocyte can never be stimulated; therefore the thymocyte can never express CD25.
Your answers told me lots of things. It spoke about cell markers expressing cell markers. It spoke about maturation and lineage markers. But your answers could not make the jump from the theory to the explanation required of you.
Now I believe that many of you are using the same old method of studying that you used last semester and last year, i.e. memorising. I need to tell you that memorising will not work in Immunology. You have to apply your knowledge. Unless you are prepared to change, and unless you do change, you will have a problem in performing well in any assessment.
Please do come see me for any help that I can offer.
The test comprised just 5 questions. Yes I concede that the question on Ab structure was trickery but that was done deliberately to test your knowledge. You were/are supposed to be aware of the fact that IgM is a pentamer. When I questioned you in class during the practical session, you all agreed that you knew this. But knowing this fact and applying it are two different things.
Question 4 was done very poorly. I really emphasized in class that cells express cell markers. CD1 is a maturation marker and is only expressed by thymocytes. Thymocytes are immature T cells found only in the thymus. Thats 2 marks out of 5. The remaining 3 marks comes from stating that CD25 is only expressed by an activated/stimulated cell; a thymocyte can never be stimulated; therefore the thymocyte can never express CD25.
Your answers told me lots of things. It spoke about cell markers expressing cell markers. It spoke about maturation and lineage markers. But your answers could not make the jump from the theory to the explanation required of you.
Now I believe that many of you are using the same old method of studying that you used last semester and last year, i.e. memorising. I need to tell you that memorising will not work in Immunology. You have to apply your knowledge. Unless you are prepared to change, and unless you do change, you will have a problem in performing well in any assessment.
Please do come see me for any help that I can offer.
Monday, March 7, 2011
Foundation Immunology tutorials
I have been asked to post the answers to the tut I have given you. The problem with that, is that you will learn the answers and not know how to approach answering these type of questions. Ideally you should be working out the answers, asking me to have a look at it, and then I would help you in knowing how to approach answering the questions. So I am very hesitant in posting answers.
What I will do, is guide you, on how to attempt the questions, and hopefully, help you understand the questions asked. So here goes:
1. Write 2 sentences to show the relationship between TC, CD4, CD8, MHC class II and APC.
NB! Some components are missing
Your answer should include ONLY 2 sentences, and each sentence should explain one relationship. Remember that cells express cell markers, and that cell markers interact with each other. So your answer should go something like this: ---- cell expressing -------- interacts with ------- expressed by -------
Then blanks will either be the cell type of the cell marker.
You already know that Tc expresses CD8, TH expresses CD4, MHC class II is expressed by APC’s and that MHC class I is expressed by nucleated cells.
So your final answer should be:
TC expressing CD8 interacts with MHC class I expressed by nucleated cells
And vice versa……
2. Supply immunologically sound reasons why booster shots of vaccines are necessary.
This questions relates indirectly to the differences between the primary and secondary IR.
Now booster shots of vaccines are the second and subsequent doses of vaccines. We all know that most vaccines are given more than once. A classic example is measles.
A vaccine is an altered version of the antigen that remains antigenic but is no longer pathogenic. So when it is given twice, it will induce a secondary IR. We know that more Ab are produced in the secondary IR and the Ab produced have a greater affinity. Surely these are good attributes to have. Yes indeed, I want those AB!!!
These are the only questions I expect you to have a problem with. Please see me if you need further help.
What I will do, is guide you, on how to attempt the questions, and hopefully, help you understand the questions asked. So here goes:
1. Write 2 sentences to show the relationship between TC, CD4, CD8, MHC class II and APC.
NB! Some components are missing
Your answer should include ONLY 2 sentences, and each sentence should explain one relationship. Remember that cells express cell markers, and that cell markers interact with each other. So your answer should go something like this: ---- cell expressing -------- interacts with ------- expressed by -------
Then blanks will either be the cell type of the cell marker.
You already know that Tc expresses CD8, TH expresses CD4, MHC class II is expressed by APC’s and that MHC class I is expressed by nucleated cells.
So your final answer should be:
TC expressing CD8 interacts with MHC class I expressed by nucleated cells
And vice versa……
2. Supply immunologically sound reasons why booster shots of vaccines are necessary.
This questions relates indirectly to the differences between the primary and secondary IR.
Now booster shots of vaccines are the second and subsequent doses of vaccines. We all know that most vaccines are given more than once. A classic example is measles.
A vaccine is an altered version of the antigen that remains antigenic but is no longer pathogenic. So when it is given twice, it will induce a secondary IR. We know that more Ab are produced in the secondary IR and the Ab produced have a greater affinity. Surely these are good attributes to have. Yes indeed, I want those AB!!!
These are the only questions I expect you to have a problem with. Please see me if you need further help.
Friday, March 4, 2011
micro3 tut answers
CTA sugars Neisseria
Bulls eye colonies Yersinia enterocolitica
CNA agar Staphylococcus
Sorbitol MacConkey E coli 0157H7
Alkaline peptone water Vibrio
Red colonies with black centres Salmonella
Coag neg MSA neg DNAse neg novobiocin R S saprophyticus
Kauffman White scheme Salmonella
Lancefield grouping Streptococcus
Impetigo S aureus
Bacitracin R halophile S aureus
MRSA S aureus
CAMP reaction with arrowhead haemolysis S agalactiae
Bacitracin S, Beta haemolytic GPC S pyogenes
Draughtsman colonies S pneumoniae
Increased haemolysis in CO2 Streptococcus
R to trimeth and sulphamethoxazole S pyogenes
GN diplococcic Neisseria
Opthalmia neonatorium N gonorrhoeae
Kidney shaped IC to neutrophils Neisseria
Growth on BA/CHOC at room temp, and NA at 37 degrees Non pathogenic Neisseria, i.e. commensals
Anorectal, conjunctival and oropharyngeal specimens N gonorrhoeae
MTM agar Neisseria
NYC agar Neisseria
HUS E coli 0157H7 or EHEC
CIN agar Y enterocolitica
Non motile at 37, motile at room temp Yesrsinia except pestis
Bulls eye colonies Yersinia enterocolitica
CNA agar Staphylococcus
Sorbitol MacConkey E coli 0157H7
Alkaline peptone water Vibrio
Red colonies with black centres Salmonella
Coag neg MSA neg DNAse neg novobiocin R S saprophyticus
Kauffman White scheme Salmonella
Lancefield grouping Streptococcus
Impetigo S aureus
Bacitracin R halophile S aureus
MRSA S aureus
CAMP reaction with arrowhead haemolysis S agalactiae
Bacitracin S, Beta haemolytic GPC S pyogenes
Draughtsman colonies S pneumoniae
Increased haemolysis in CO2 Streptococcus
R to trimeth and sulphamethoxazole S pyogenes
GN diplococcic Neisseria
Opthalmia neonatorium N gonorrhoeae
Kidney shaped IC to neutrophils Neisseria
Growth on BA/CHOC at room temp, and NA at 37 degrees Non pathogenic Neisseria, i.e. commensals
Anorectal, conjunctival and oropharyngeal specimens N gonorrhoeae
MTM agar Neisseria
NYC agar Neisseria
HUS E coli 0157H7 or EHEC
CIN agar Y enterocolitica
Non motile at 37, motile at room temp Yesrsinia except pestis
Thursday, March 3, 2011
haemolytic disease of the newborn (HDN)
This is a disease of the newborn characterised by massive intravascular and extravascular lysis of red blood cells due to a Rhesus incompatibility.
This is what happens in HDN:
PS Please read Rhesus typing first, in order to appreciate this
a mom is Rhesus negative, pregnant with a baby from a Rhesus positive father. In most cases the baby will be Rhesus positive.
The situation i am going to describe is what happens in a normal pregnancy, no trauma, no placenta abruptio, etc
The mom's blood circulates through the baby, and never vice versa
So the D antigen in the baby never comes into contact with the mom'c immune system.
During delivery, when the placenta breaks, there is mixing of the baby's and mom's blood. D from the baby comes into contact with the mom's immune system and she, naturally, produces anti D.
If, at this stage, nothing is done, the antiD will remain in the mom, quietly waiting.....
In the next pregnancy from the same father, mom's blood is circulating through the baby. AntiD from the mom will now agglutinate the D of/in the baby, leading to HDN.
Can you imagine the consequences of this.....this tiny little baby, still in utero, having all or almost all its RBC haemolysed? so is there no hope for little Keith??????
weel if this situation was allowed to develop, doctors can do an exchange transfusion either in utero or after the baby is born. Basically quite dangerous but there have been some successes. The baby's blood is removed, a little at a time, and fresh blood from a donor is transfused into the baby. All sorts of possible transfusion reactions , but that will keep for another post. Ta Ta
This is what happens in HDN:
PS Please read Rhesus typing first, in order to appreciate this
a mom is Rhesus negative, pregnant with a baby from a Rhesus positive father. In most cases the baby will be Rhesus positive.
The situation i am going to describe is what happens in a normal pregnancy, no trauma, no placenta abruptio, etc
The mom's blood circulates through the baby, and never vice versa
So the D antigen in the baby never comes into contact with the mom'c immune system.
During delivery, when the placenta breaks, there is mixing of the baby's and mom's blood. D from the baby comes into contact with the mom's immune system and she, naturally, produces anti D.
If, at this stage, nothing is done, the antiD will remain in the mom, quietly waiting.....
In the next pregnancy from the same father, mom's blood is circulating through the baby. AntiD from the mom will now agglutinate the D of/in the baby, leading to HDN.
Can you imagine the consequences of this.....this tiny little baby, still in utero, having all or almost all its RBC haemolysed? so is there no hope for little Keith??????
weel if this situation was allowed to develop, doctors can do an exchange transfusion either in utero or after the baby is born. Basically quite dangerous but there have been some successes. The baby's blood is removed, a little at a time, and fresh blood from a donor is transfused into the baby. All sorts of possible transfusion reactions , but that will keep for another post. Ta Ta
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